The present invention concerns methods of fabricating integrated circuits, particularly methods of forming interconnects from copper and other metals.
Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators typically use various techniques, such as layering, doping, masking, and etching, to build thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.
Interconnecting millions of microscopic components typically entails covering the components with an insulative layer of silicon dioxide, etching small holes in the insulative layer to expose portions of the components underneath, and digging trenches in the layer to define a wiring pattern. Then, through metallization, the holes and trenches are filled typically with aluminum, to form line-like aluminum wires between the components. The aluminum wires are typically about one micron thick, or about 100 times thinner than a human hair.
Silicon dioxide and aluminum are the most common insulative and conductive materials used to form interconnections today. However, at sub-micron dimensions, that is, dimensions appreciable less than one micron, aluminum and silicon-dioxide interconnection systems present higher electrical resistances and capacitances which waste power and slow down integrated circuits. Moreover, at these smaller dimensions, aluminum exhibits poor electromigration resistance, a phenomenon which promotes disintegration of the aluminum wires at certain current levels. This ultimately undermines reliability, not only because disintegrating wires eventually break electrical connections but also because aluminum diffuses through surrounding silcon-dioxide insulation to form short circuits with neighboring wires. Thus, at submicon dimensions, aluminum and silicon-dioxide interconnection systems waste power, slow down integrated circuits, and compromise reliability.
Copper appears, because of its lower electrical resistivity and higher electromigration resistance to be a promising substitute for aluminum. And, many polymers, for example, fluorinated polyimides, because of their lower dielectric constants, appear to be promising substitutes for silicon dioxide. Thus, a marriage of copper with these polymers promises to yield low-resistance, low-capacitance interconnective structures that will improve the efficiency and speed of integrated circuits.
Unfortunately, copper reacts with these polymers to form conductive copper dioxide within these polymers, reducing their effectiveness as low-capacitance insulators and ultimately leaving the copper-polymer promise of superior efficiency and speed unfulfilled.
To address these and other needs, the inventor has developed methods of making copper-polymer interconnection systems with reduced copper oxide. Specifically, one method uses a non-acid-based polymeric precursor, such as ester, instead of the typical acid precursor, to form a polymeric layer, and then cures the layer in a reducing or non-oxidizing atmosphere, thereby making the layer resistant to oxidation. Afterward, a zirconium, hafnium, or titanium layer is formed on the polymeric layer to promote adhesion with a subsequent copper layer. With the reduced formation of copper oxide, the method yields faster and more efficient copper-polymer interconnects.
Moreover, reducing copper-dioxidation facilitates micron and sub-micron spacing of polymer-insulated copper conductors, which would otherwise require spacings of 10 or more microns. Accordingly, another aspect of the invention is an integrated circuit including at least two conductors which are separated by no more than about one micron of a polymeric insulator. Thus, the inventor provides a method that not only yields copper-polymer interconnects of superior speed and efficiency, but also yields integrated circuits with unprecedented spacing of copper-polymer interconnects.